The present invention relates to the use of a structure based on poly(dimethylketene) and to the objects comprising this structure.
More specifically, the invention relates to the use of a structure comprising at least one layer of a polymer (A) comprising:
the units (A1) 
and the units (A2) 
such that the A2/(A1+A2) molar ratio is between 0 and 30%.
The prior art GB 893,308 discloses polymers comprising 81.6% by weight of units (A1) obtained by polymerization of dimethylketene 
in the presence of aluminium bromide. The polymer powder thus obtained is subjected to successive extractions with various solvents at boiling point, namely acetone, ether and toluene. There remains 81.6% of the starting polymer which cannot be extracted with toluene, its melting temperature being 255xc2x0 C. Diffraction shows a crystalline structure. These polymers were not converted into films.
The prior art U.S. Pat. No. 3,321,441 discloses the polymerization of dimethylketene in the presence of a strong base and the production of a polymer composed of units (A2).
None of these documents discloses the barrier properties of films of polymer (A). The Applicant Company has discovered that films made of polymer (A) are good barriers to gases, to hydrocarbons and to petrols for cars.
The Applicant Company has also discovered that films made of polymer (A) of the invention are very good barriers to oxygen and that this property is not very sensitive to the relative humidity (RH). Films made of EVOH, a copolymer of ethylene and of vinyl alcohol (also known as saponification products of copolymers of ethylene and of vinyl acetate), have an oxygen barrier level of the same order as those composed of the polymer (A), provided that the relative humidity does not exceed 50%. Beyond 50% RH, EVOH to a large extent loses its barrier properties.
The structure used in the invention can be monolayer, that is to say be only one layer of the polymer (A).
The structure used in the invention can be multilayer, that is to say that it comprises at least one layer of the polymer (A) and at least one layer of the polymer (B), it being possible for a binder to be positioned between the layers (A) and (B).
According to another form, the structure used in the invention can respectively comprise a polymer (C), the polymer (A) and a polymer (B), it being possible for a binder to be positioned between the layers (C) and (A) and/or between the layers (A) and (B).
The monolayer structure of the invention can be a film.
The present invention also relates to the objects manufactured with any one of the preceding mono- or multilayer structures.
The present invention also relates to packagings and hollow bodies, such as pipes, bottles and containers, comprising any one of the preceding structures. The packagings are, for example, bags and sachets which are obtained with the said mono- or multilayer structures existing in the form of a mono- or multilayer film. Particularly advantageous hollow bodies are petrol tanks for cars. These tanks can have a structure such that the layer of polymer (A) is either in direct contact with the petrol or is not in direct contact with the petrol. Particularly advantageous pipes are those used to convey petrol in service stations between the storage tanks and the tankers from which these tanks are filled or the pipes which connect the storage tanks and the pumps for distribution to vehicles, such as cars. Other particularly advantageous pipes are those which transfer petrol between the tank of the car and the engine. Other particularly useful pipes are those in which the polymer (A) is the external layer; they can be incorporated in the floors and walls of habitations in order to provide heating thereto.
The invention will now be described in detail.
Dimethylketene can be obtained by the pyrolysis of isobutyric anhydride. This synthesis has been disclosed in Patents GB 965,762, FR 1,381,831 and U.S. Pat. No. 3,201,474. It has also been described in the following articles:
M. Mugno, M. Bornengo, Chim. Ind. (Milan 46, 1, 5-9, 1964)
G. F. Pregaglia, M. Binaghi, Makromol. Syn., 3, 150-160, 1968.
This pyrolysis can be carried out between 550xc2x0 C. and 675xc2x0 C. under an absolute pressure of between 30 and 40 mm Hg (3960 and 5280 Pa).
The polymerization of the dimethylketene to produce the polymer (A) can be carried out in the presence of a catalyst of formula Al(R1)3-mXm in which
X is a halogen atom
R1 denotes an alkyl, aryl, cycloalkyl or alkoxy group or a hydrogen atom.
Mention may be made, by way of examples, of AlCl2C2H5, AlCl(C2H5)2, AlC6H5Cl2, Al(OC3H7)Br2, AlBr3, AlCl3 or their dimers or the sesquihalides of the type AlC2H5Cl2.Al(C2H5)2Cl.
Use may also be made of another catalyst, such as an organometallic compound of a metal from the second column of the Table of the Elements or the complexes of these compounds with ethers. Mention may be made, for example, of dialkylberylliums, alkylberyllium monohalides, dialkylmagnesiums, alkylmagnesium monohalides, dialkylzincs and alkylzinc monohalides. The polymerization can be carried out between xe2x88x92100xc2x0 C. and +40xc2x0 C., optionally in the presence of a solvent, provided the solvent does not react with the monomer and does not decompose the catalyst. Mention may be made, by way of examples, of aliphatic, cyclic or aromatic hydrocarbons and solvents having a high dielectric constant, such as nitrobenzene, dichloromethane, 1,1,1,2-tetrachloroethane and 1,1-dichloroethylene. This polymerization is also disclosed in GB 987,370 and GB 893,908, the contents of which are incorporated in the present application. It is also described in the following articles:
G. F. Pregaglia, M. Peraldo, M. Binaghi, Gazz. Chim. Ital., 92, 488-500, 1962.
G. F. Pregaglia, M. Binaghi, Makromol. Syn., 3, 150-165, 1968.
G. Natta, G. Mazzanti, G F. Pregaglia, M. Binaghi, M. Peraldo, J. Am. Chem. Soc., Vol. 82, 4742-4743, 1960.
It would not be departing from the scope of the invention if the polymer (A) also contained units (A3) 
it being possible for the content of (A3) to be from 0 to 5 mol per 100 mol of (A1).
The proportion of (A2) in the polymer (A) depends on the polymerization conditions, in particular on the polarity of the solvent.
The proportion of (A2) is usually (in moles) from 5 to 15%.
The polymer (A) is thermoplastic and has the following properties:
thermal decomposition: beginning of decomposition from 300xc2x0 C. without stabilizer, obtained by thermogravimetry at 10xc2x0 C./min.
relative density: 1.28
melting temperatures at 230 and 255xc2x0 C., peak measured by differential enthalpy analysis (20xc2x0 C./min under nitrogen).
intrinsic viscosity in solution at 20xc2x0 C.: from 0.5 to 3 (for a 0.5 g/dl solution in meta-cresol).
The polymer (A) can be converted into a film by the usual means for thermoplastics, such as the blown-film process, pressing, calendering or slot die extrusion. Hollow bodies made of (A) can be produced by extrusion (pipes) or extrusion blow-moulding for hollow bodies.
Films made of polymer (A) and with a thickness of 5 to 150 xcexcm have a variation in the permeability to oxygen (measured according to ASTM Standard D 3985-81) as a function of the relative humidity (RH) such that:
the permeability at 75% RH/permeability at 0% RH ratio is between 1.2 and 2;
the permeability at 95% RH/permeability at 0% RH ratio is between 1.4 and 2.5.
For EVOH, these values are between 4 and 15 and between 8 and 20 respectively.
The permeability is expressed in cm3 per m2 for 24 hours for a pressure difference of 105 Pa and for a given thickness.
To compare films of different thicknesses, the thickness is corrected in proportion (permeabilityxc3x97thickness=constant).
The permeability to oxygen in cm3/m2, 24 h, 105 Pa, 70 xcexcm, is of the order of: 0.15 to 0.20 at 23xc2x0 C. and 0% RH
0.2 to 1 at 23xc2x0 C. and 75% RH.
These values decrease as the proportion of (A2) in (A) decreases.
With regard to multilayer structures, the polymer (B) can be chosen, for example, from polyolefins, polystyrenes, polyamides, polycarbonate, PVC, PVDF and saturated polyesters, such as PET and PBT.
Mention may be made, by way of examples, of the structures:
(A)/PA-6, (A)/(PA-6,6), (A)/(PA-6/6,6), (A)/PA-11, (A)/PA-12, (A)/PE or (A)/polypropylene.
These structures have respective thicknesses of, for example, 5 to 30 xcexcm/15 to 100 xcexcm, if they are flexible films for the manufacture of sachets.
With regard to coextruded pipes, the thicknesses can be 5 to 10,000 xcexcm/0.5 to 5 mm.
With regard to hollow bodies, the thicknesses depend on the volume and can be several millimetres. It is recommended to position a binder between the layers (A) and (B).
Mention may be made, by way of examples of binder, of:
polyethylene, polypropylene, copolymers of ethylene and of at least one xcex1-olefin, or mixtures of these polymers, all these polymers being grafted with unsaturated carboxylic acid anhydrides, such as, for example, maleic anhydride. Use may also be made of mixtures of these grafted polymers and of these ungrafted polymers.
copolymers of ethylene with at least one product chosen from (i) unsaturated carboxylic acids, their salts or their esters, (ii) vinyl esters of saturated carboxylic acids, (iii) unsaturated dicarboxylic acids, their salts, their esters, their hemiesters or their anhydrides, or (iv) unsaturated epoxides, it being possible for these copolymers to be grafted with unsaturated dicarboxylic acid anhydrides, such as maleic anhydride, or unsaturated epoxides, such as glycidyl methacrylate.
It is also possible to add, to one or to each of the layers, a product which improves their adhesion, without having to use a binder layer. This product can be the binder described hereinabove.
Examples of binders are disclosed in Patents EP 802,207, EP 816,460, EP 837,080 and EP 742,236.
With regard to (A)/binder/polyolefin structures, particularly useful binders are those disclosed in EP 816,067 and used for structures having a polyketone layer of formula 
in which D denotes an unsaturated monomer having at: least 3 carbon atoms, the x/y ratio being at least 2.
The 
units are distributed randomly in the polyketone chain.
The number-average molar masses can be between 1000 and 200,000, advantageously between 20,000 and 90,000 (measured by gel permeation chromatography). The melting temperatures can be between 175 and 300xc2x0 C., generally between 200 and 270xc2x0 C.
Syntheses of these polyketones are disclosed in U.S. Pat. Nos. 4,843,144, 4,880,903 and 3,694,412.
The binder can be:
either a thermoplastic polymer comprising at least one hydroxyl functional group which can be a copolymer having a hydroxyl functional group, a mixture of polymers each having at least one hydroxyl functional group or a mixture of a polymer having at least one hydroxyl functional group with another polymer or any other combination,
or a thermoplastic polymer comprising at least one epoxide functional group which can be a polymer having an epoxide functional group, a mixture of polymers each having at least one epoxide functional group or a mixture of a polymer having at least one epoxide functional group with another polymer or any other combination,
or a thermoplastic polymer comprising ethylene units and at least one alkyl(meth)acrylate unit.
With regard to (A)/binder/polyamide structures, binders which are particularly used are copolyamides. Mention may be made, for example, of:
PA-6/6,6, copolymer of caprolactam, of hexamethylenediamine and of adipic acid
PA-6/6,6/12, copolymer of caprolactam, of hexamethylenediamine and of adipic acid, and of lauryllactam
PA-6/12, copolymer of caprolactam and of lauryllactam
PA-6,12, copolymer of hexamethylenediamine and of dodecanedioic acid.
With regard to (C)/(A)/(B) structures, the polymer (C) can be chosen from the polymers cited for (B).